It is well known in the fluid power and control industry to utilize delta pressure regulating valves (hereinafter ".DELTA.P valves") to control or regulate the pressure differential between a high pressure side and a low pressure side of a fluid system component such as, for example, a pump, a flow control valve, an accumulator, a heat exchanger, etc. One known application of such .DELTA.P valves is shown in FIG. 1, which illustrates a typical arrangement for a fuel control system 10 for a gas turbine engine. The system 10 includes a fuel pump 12, a servo metering valve 14 having a high pressure side 16 and a low pressure side 18, a .DELTA.P valve 20 for maintaining a constant pressure differential between the high and low pressure sides 16 and 18, and a bypass passage 22 for bypassing flow from the high pressure side 16 though the .DELTA.P valve 20 to an inlet side 24 of the pump 12. The servo metering valve 14 will typically be designed to deliver a fuel flow rate to an engine that is linearly proportional to a command current signal from an electronic engine control (not shown). The constant differential pressure between the high and low pressure sides 16 and 18 provided by the .DELTA.P valve 20 allows for the linear relationship to be maintained between the command current signal and the fluid flow rate delivered to the engine by the servo metering valve 14.
FIG. 2 shows a more detailed representation of at least one known type of .DELTA.P valve 20A for use in a fluid system, such as the fuel control system 10 shown in FIG. 1. The .DELTA.P valve 20A includes a cylindrical valve piston or spool 30 that translates within a cylindrical bore 32 formed in a sleeve 34, which is typically provided as a matched set with the valve spool 30. The sleeve 34 is part of a valve housing 35 that includes a high pressure port 36 that is connected to the high pressure side 16 of the servo valve 14, a low pressure port 38 that is connected to the low pressure side 18 of the servo valve 14, and a bypass control port 40 that is connected to the bypass passage 22 to direct a modulated fuel flow thereto from the high pressure port 36. A cylindrical valve stem 41 is connected to the valve spool 30 for translation therewith, and extends from the spool 30 through the bore opening 66 to outside of the bore 32. One end 42 of the valve spool 30 is acted on by the fuel pressure on the high pressure side 16 of the servo valve 14, and the other end 44 of the valve spool 30 is acted on by the fuel pressure on the low pressure side 18 of the servo valve 14. Thus, the valve spool 30 senses the pressure differential across the servo valve 14. A helical compression, delta pressure spring 46, acting through a spring retainer or seat 48 engaged with the valve stem 41, serves to bias the valve spool 30 toward a delta pressure set point (hereinafter ".DELTA.P set point) where the force on the valve spool 30 created by the high pressure acting on the end 42 is balanced by the force of the spring 46 and the low pressure acting on the end 44 and the stem 41. An adjustment screw or spacers (not shown) may be used to set the preload of the spring 46 and, thereby, the .DELTA.P set point.
The valve spool 30 modulates the pressure differential by varying a metering orifice or flow control area 52 between the high pressure port 36 and the bypass port 40 to modulate a fuel flow to the bypass flow passage 22. More specifically, if the valve spool 30 senses excessive delta pressure, the valve spool 30 will be forced toward the low pressure port 38, compressing the delta pressure spring 46 and enlarging the flow control area 52 to the bypass flow port 40. This increases the force of the spring 46 and decreases the pressure on the high pressure side 16, thereby restoring the desired .DELTA.P set point. Conversely, if the valve spool 22 senses insufficient delta pressure, the valve spool will move toward the high pressure port 36, decompressing the delta pressure spring 46 and reducing the flow control area 52 to the bypass flow port 40. This decreases the force of the spring 46 and increases the pressure on the high pressure side, thereby restoring the desired .DELTA.P set point.
It is known for fluid systems, such as the fuel control system 10, to become unstable when there is insufficient damping in the system and if one or more of the components, such as the valve 20A, is excited at a resonate frequency. While various methods and devices exist to increase the damping of fluid systems and components, they can often add excess cost and/or be difficult to incorporate due to pre-existing constraints in envelope size and hardware configuration. Accordingly, there is always room for improvement.